1. Field of the Invention
Heretofore, processes of the prior art wherein suspension fertilizers were produced by acidulation of phosphate rock used either nitric acid or sulfuric acid as the primary acidulating reagent with, in some instances, phosphoric acid being used in conjunction therewith as an ancillary acidulating reagent. A principal consideration of the instant invention is associated with the fact that suspension fertilizers, produced by the practice of the teachings of the prior art, which derive substantial proportions of their P.sub.2 O.sub.5 content from phosphate rock necessarily have been restricted to being products of low phosphate content because of the low P.sub.2 O.sub.5 and high impurity content of the phosphate rock used as the feed therein. This restriction improsed upon the products produced by such prior art processes was also found to be of necessity in order to avoid occurrence of high viscosity characteristics therein, which high viscosity characteristics tend to destroy the fluidity of such suspensions and render the transfer properties thereof, either by gravity or pumping distribution to the soil, rather impractical or indeed, impossible. It will be appreciated by those skilled in the art that suspension fertilizers with such low analysis have a very distinct economic disadvantage as compared with higher-analysis products because costs of handling, freight, storage, and application are higher per unit of plant nutrient, all of which are factors of increasingly greater importance as costs associated therewith continue to escalate at a rate faster than certain other considerations, as for example, the costs of production of said fertilizers.
2. Description of the Prior Art
At the present time, because of the state of the art developed in view of and in response to said principal consideration supra, there are available a number of methods and means which utilize in one way or another the art of producing fertilizers by acidulation of phosphate rock, some of which are represented by the investigations, teachings, and disclosures set forth in the following patents: U.S. Pat. Nos. 3,507,641, Richmond et al, Apr. 21, 1970, 3,619,162, Pottgiesser et al, Nov. 9, 1971, and British Pat. No. 1,165,257, Palgrave et al, Sept. 24, 1969.
As has been noted above, numerous prior art investigators have discovered, taught, and disclosed a plethora of methods and/or means for acidulation of phosphate rock. In Great Britain in 1969, Palgrave et al ('257 supra) reacted phosphate rock with nitric acid and neutralized the acidulate with ammonium hydroxide. Subsequently, potassium chloride was added to the resulting neutralized acidulate in order to produce a 8.5-8.3-8.5 (N--P.sub.2 O.sub.5 --K.sub.2 O) grade fluid fertilizer.
In 1970, Richmond et al ('641 supra) reacted phosphate rock with phosphoric acid and then with sulfuric acid. The resulting acidulate was subsequently neutralized with anhydrous ammonia to produce a 7-21-0 (N--P.sub.2 O.sub.5 --K.sub.2 O) grade slurrey fertilizer. In later investigations Pottgiesser et al ('162 supra) produced a 13.5-6-0 (N--P.sub.2 O.sub.5 K.sub.2 O) grade slurry by reacting nitric acid with phosphate rock and subsequently feeding the resulting slurry into a body of preneutralized solution maintained at pH 7-10 by addition thereto of aqua ammonia.
There is no suggestion in the teachings of any of the above prior art references of the viable technique of the instant invention for the practice of processes effective in the production of zero-nitrogen phosphate grade or zero-nitrogen phosphate-potassium grade suspension fertilizers by utilizing wet-process phosphoric acid as the exclusive acidulating agent therein.